Transfer switch for tap changers for regulating transformers



W. BREUER May 31, 1966 TRANSFER SWITCH FOR TAP CHANGERS FOR REGULATING TRANSFORMERS 2 Sheets-Sheet 1 Filed April 25, 1965 y 1966 I w. BREUER Y 3,254,296

TRANSFER SWITCH FOR TAP CHANGERS FOR REGULATING TRANSFORMERS Filed April 25, 1963 2 Sheets-Sheet 2 .Bmax

:BmczX g;=f/t) /NI/NIU/PI N MMM United States Patent 3,254,296 TRANSFER SWITCH FOR TAP CHANGERS FOR REGULATIN G TRANSFORMERS Wolfgang Brener, Regensburg, Germany, assignor to Maschinenfabrik Reinhausen Gebruder Scheubeck K.G., Regensburg, Germany Filed Apr. 25, 1963, Ser. No. 275,583 Claims priority, appligaltitsnzi Ge7rmany, May 25, 1962,

6 Claims. of. 323-435 fer switches therefor, having means to reduce the transient recoverey voltage between the contacts, and to thus facilitate extinction of the arcs drawn between parting contacts of the transfer switches.

Still another object of the invention is to provide improved tap-changing regulating transformers, and transfer switches therefor, wherein arc-quenching is effected by compact saturable reactor means rather than by bulky arc-chute means.

A further object of this invention is to provide compact tap-changing regulating transformers, and transfer switches therefor, known as Jansen-type regulating transformers, and Jansen-type transfer switches, respectively, which transfer switches have a drastically increased current switching capacity.

Another object of this invention is to provide Jansentype tap-changing regulating transformers having improved high switching capacity FLAG transfer switches, PENNANT transfer switches, or FLAG-PENNANT transfer switches. PENNANT transfer switch and FLAG-PENNANT transfer switch are generally used to designate particular designs of transfer switches for transformers. These terms have also been fully explained and defined in the copending patent application of Alexander Bleibtreu, filed January 31, 1963; Ser. No. 255,291 for Transfer Switch for Tap Changers for Regulating Transformers, now U.S. Patent 3,174,097.

Tap-changing regulating transformers include selector switches and transfer switches. The former serve the purpose of selecting a particular tap on a tapped trans' former winding intended to be connected into an electric circuit. Selector switches are not required to interrupt, or close, on current carrying circuits. This task is left to the transfer switches. The latter perform all switch- .ing operations under load, including switching of overload currents. Hence all arcing is kept away from the selector switches and occurs only at the transfer switches.

It is, therefore, another object of this invention to provide transfer switches capable of handling considerable or large amounts of power, and in particular of handling high currents, without being damaged by arcing incident to switching operations.

Transfer switches according to this invention may be constructed either for single phase service or for polyphase service.

The above objects and additional objects and advantages of the invention will become more'apparent from the ensuing description of the invention and of a specific The terms FLAG transfer switch,

embodiment thereof when read in connection with the accompanying drawings wherein:

FIG. 1 is a diagrammatic representation of a single phase of a tap-changing regulating transformer embodying the present invention including its transfer switch, its selector switch having been omitted for the sake of simplicity;

FIG. 2a shows, occurring incident to a tap-changing operation;

FIG. 2b shows, diagrammatically, another current transient occurring incident to a tap-changing operation;

FIG. 20 shows, diagrammatically, a voltage transient occurring incident to the same tap-changing operation to which FIGS. 2a and 2 h refer;

FIG. 2d shows, diagrammatically, the transient recovery voltage occurring across a pair of parting main contacts of the transfer switch during the same tap-changing operation to which FIGS. 2a to 2c refer; and

FIG. 3 shows the magnetic flux in a saturable reactor forming an integral part of the circuitry of FIG. 1 plotted against the magnetizing current.

Referring now to the drawings, and more particularly to FIG. 1 thereof, reference character T has been applied ,to indicate a portion of a tapped transformer winding,

including the taps, or tap terminals, A and B. As a general rule a selector switch is interposed between the taps, or tap terminals, of a tapped transformer winding and the transfer switch which is associated with the tapped transformer winding, but in drawing FIG. 1 the selector switch has been omitted and the tapped transformer winding T has been shown as being directly connected to a transfer switch which includes switches 1, 2; 3; 4; 5, 6. Switches 1, 2 and 5, 6, respectively, are main switches each comprising two pairs of cooperating separable contacts. The movable contacts of switches 1, 2 and 5, 6 are adapted to be operated sequentially. The transfer switch further comprises a pair of switch-over switches 3, 4, each comprising a plurality of pairs of cooperating separable contacts. The movable contacts of switch 3 are gang operated to open and close simultaneously. To the same end the movable contacts of switch 4 are gang operated. The contacts of switch-over switch 3 define a plurality of parallel current paths. In a similar fashion, the contacts of switch-over switch 4 define a plurality of parallel current paths, the number of parallel current paths defined by switches 3 and 4 being equal. Reference characters R, and R have been applied to indicate a pair of switch-over resistors. Each switch-over resistor R and R is sub-divided into four sub-resistors R R .,'respectively. Tap A is conductively connected to main switch 1, 2 by the intermediary of a saturable reactor L,,. In a like fashion tap B is conductively connected to main switch 5, 6 by the intermediary of a saturable reactor L Each saturable'reactor L L comprises a ferrous magnetizable core providing a complete magnetic flux path for the magnetic flux established by the winding of the respective saturable reactor. Each saturable reactor L L has one end conductively connected to one of taps A, B and another end conductively connected to one of the pair of main switches 1, 2 and 5, 6, respectively. The latter end of each saturable reactor L,,, L, is conductively connected to one of the subresistors R and R by the intermediary of magnetizing current control resistors R and R The latter are resistors having a high ohmic value being a multiple of that of resistors R R As illustrated in FIG. 1 each pair of cooperating contacts of switches 1, 2; 3; 4; 5, 6 comprises a movable contact and a stationary contact. The stationary contacts of the transfer switch are arranged at the transformer side of the latter, and all the movable contacts of the transfer switch are conductively connected diagrammatically, a current transient by an appropriate lead to a point M. The latter may represent the load.- Assuming that winding T is a portion of a Y-connected three phase transformer, then point M may be considered to be the neutral point of the system. Taps A and B are further conductively connected to switch-over resistors R and R of which each comprises four sub-resistors connected in parallel. The current path through each sub-resistor is controlled by a pair of cooperating contacts pertaining to either of the two switch-over switches 3 and 4.

In the rest position of the circuitry of FIG. 1 the contacts pertaining to both switch-over switches 3 and 4 are open, and the contacts pertaining to one of the main switches 1, 2 and 5, 6, respectively, are closed, while the contacts pertaining to the other of the main switches are open. The pair of closed contacts of switch 1, 2 establishes a direct current path including saturable reactor L between tap A and the above mentioned point M. The load current flowing through saturable reactor L completely saturates the ferrous core thereof. The voltage drop along saturable reactor L is equal to the ohmic voltage 'drop plus the voltage drop caused by the leakage flux in that saturable reactor. Both saturable reactors L and L are designed to have but a very small total voltage drop. The same which has been said above in regard to tap A and main switch 1, 2 applies to tap B and main switch 5, 6 when the latter is closed while the former is open. Assuming that the pair of contacts of main switch 1, 2 are initially closed, and that the pair of contacts of main switch 5, 6 are initially open. In other words, it is assumed that tap A is initially included into the load circuit of the tap-changing transformer and that tap B is not included in that circuit. The operation of the circuitry of FIG. 1 will now be explained by setting forth the consecutive steps involved in changing from tap A to tap B.

The first such step is opening of the pair of contacts 1 of main switch 1, 2. As a result of the separation of this pair of contacts, the entire load current is henceforth carried by the pair of contacts 2 of switch 1, 2. Thereafter the group of contacts 3 is being closed and substantially simultaneously the pair of contacts 2 opened. As a result of separating the pair of cooperating contacts 2 an arc is kindled between these contacts. This arc subsists approximately until the time of current zero at which time the magnetization of the saturable reactor L is reversed, causing the latter to intervene in the switching operation by virtue of the inductive voltage U resulting from the reversal of magnetization.

Referring now to FIGS. 2a to 2d, the trace marked i represents the current flowing through saturable reactor L and the pair of contacts 2 of switch 1, 2 which are serially connected with the saturable reactor L The path of this current has also been indicated in FIG. 1 by reference character i Shortly prior to the time of a natural current zero of the sinusoidal current wave i saturable reactor L which was previously saturated is being demagnetized and thereupon re-magnetized in reverse direction. Reference character t has been applied in the various figures to indicate the point of time at which the momentary value of the current i becomes smaller than the saturation current of the saturable reactor L As a result of the operation of saturable reactor L outside of the saturation region thereof its impedance to the passage of current i becomes very large. Hence the magnitude of current i becomes virtually zero, and the preponderance of the current flowing from tap A to point M flows through the current path shunting the pair of contacts 2, i.e. the current path formed by resistor R and the group of contacts of switch 3. Because of the drastic decrease of the intensity of the current i the arc kindled between the pair of contacts 2 upon separation thereof is rapidly extinguished. FIG. 2b is the trace of the current i through change-over shunt In this equation it is the voltage drop of the current flowing through resistor R B is the saturation value of the ferrous core of saturable reactor L F is the active cross-section of the ferrous core of the saturable reactor L and w is the number of turns of the winding on the saturable reactor L At a certain point of time following the time t of initiation of demagnetization of the saturable reactor L the latter will be re-magnetized in the opposite direction to its full saturation value. This point of time has been indicated in FIGS. 2a to 201 by the reference character t In FIG. 1 the voltage between the two taps has been indicated by the reference character U and the voltage across the saturable reactor L has been indicated by the reference character U During the interval of time from t to 1 the voltage U across the saturable reactor is equal to the voltage drop of the load current i across the composite resistor R The magnetizing current of the saturable reactor L flows through the magnetizing current control resistor R Since the magnetizing current of saturable reactor L is very. small, the voltage drop across resistor R is likewise very small and may be neglected.

The core of saturable reactor L, is made of a magnetizable material which has a very steepmagnetizing characteristic as clearly shown in FIG. 3.

The transient recovery voltage across the parted pair of contacts 2 is equal to the voltage drop across resistor R which is negligibly small, as mentioned above. T herefore the transient recovery voltage across the pair of separated contacts 2 will be virtually zero during the interval of time t and t during which the saturable reactor L, is unsaturated. This zero recovery voltage pause across the gap formed between the pair of separated contacts 2 is conducive to a high degree of dielectric recovery. This, in turn, minimizes the likelihood of a reignition or restrike following the reappearance at the time t;; of the recovery voltage across the separated pair of contacts 2.

FIG. 2d clearly shows the transient recovery voltage zero in the interval of time between t and t and the rise of the recovery' voltage at the time t when the saturable reactor L becomes again saturated. The saturable reactor L must be designed in such a fashion that the time t t of zero recovery voltage is sufliciently long to safely preclude any reignition or restrike of the circuit including the separated pair of contacts 2.

FIG. 20 illustrates the inductive voltage U generated by the saturable reactor L during the cycle of demagnetization and remagnetization in opposite direction. It will be noted that the voltage spikes at the times t and t are of different magnitude.

FIG. 2a shows the shunt current i to rise from zero at the time t and then to follow a more or less sinusoidal course.

- The sequence of steps following closing of the gangoperated group 3 of contacts and interruption of the arc kindled between the pair of separated contacts 2 conforms to that in a transfer switch of the FLAG type. To be over contacts closes simultaneously and the group 3 of pairs of switch-over contacts 3 opens. Each of the groups of contacts 3 and 4 may be considered as one single contact subdivided in a plurality of parallel current paths to facilitate quenching of arcs drawn at these contacts upon separation thereof. Closing of the group 4 of contacts while arcing at the group 3 of contacts still persists results in a circulating current which is superimposed upon the load current of the regulating transformer. The are current across the gaps formed between the parted pairs of contacts of group 3 is interrupted at the time of the first natural current zero following arc inception. The tap-changing operation is completed by sequential closing of the two pairs of contacts 5 and 6.

It is conceivable that the transient recovery voltage across the gaps formed between the pairs of separated contacts of group 3 is sufficiently high to cause reignition following the first natural zero of the current wave and following closing of the two pairs of contacts 5 and 6. Normally the entire load current derived from tap B is carried by the pair of contacts 6 upon closing thereof. If arcing across the gaps formed between the pairs of contacts pertaining to group 3 still continues at the time at which the cooperating pair of contacts 5 engages, a circulating current is caused to flow the magnitude of which is limited by the presence of switch-over resistor R The subdivision of the latter into a plurality of subresistors R which are connected in parallel into the current path, the current flow through each being controlled by a separate pair of separable contacts, greatly facilitates final interruption of the current through tap A. Thus rapid interruption of the above referred-to circulating current is assured.

Any change from tap B to tap A is effected in the same manner as the above described change from tap A totap B.

It will be apparent from the foregoing that the circuitry shown in FIG. 1 includes a pair of main switches 1, 2 and 5, 6. Each of these switches includes a pair of movable contacts 1, 2 and 5,' 6 adapted to be operated sequentially and to establish parallel current paths. The circuitry of FIG. 1 further comprises a pair of switchover switches 3 and 4. Each of these switch-over switches includes a plurality of gang-operated simultaneously operable movable contacts adapted to establish a plurality of current paths in parallel. Each switch-over switch 3 and 4is operatively associated with a group R. and R respectively, of switch-over resistors. Each group R R of switch-over resistors comprises a plurality of subresistors connected in parallel to form one of the groups R, and R5. Each tapA, B is connected to one of the main switches 1, 2 and 5, 6, respectively, by the intersub-resistor R remote from tap A, or tap terminal A, I

by the intermediary of magnetizing current control resistor R In a-similar fashion the end of saturable reactor L remote from tap B, or tap terminal B, is conductively connected to the end of sub-resistor R remote from tap B; or tap terminal B, by the intermediary of magnetizing current control resistor R Conceivably main switches 1, 2 and 5, 6 and switchover switches 3, 4 might be operated manually in the aforementioned proper sequence. quential operation of these switches is effected by automatic means which are well known in the art. Such means have been described, for instance, in US. Patent 2,680,790 to Bernhard Jansen, June 8, 1954 for Load Changeover Switch for Tapped Transformers, and reference may be had to this patent for additional information in regard to the aforementioned automatic switchoperating or contact-operating means.

In practice proper se- Having described the invention in detail in accordance with the requirements of the patent statutes, those skilled in the art will have no difficulties in making changes and modifications in the individual parts or their relative assembly in order to meet specific requirements or conditions. Such changes or modifications may be made without departing from the scope and the spirit of the invention as set forth in the following claims:

I claim as my invention:

1. A transfer switch for tap-changers for regulating transformers comprising in combination:

(a) a first main switch means;

(b) a second main switch means;

(0) a first switch-over switch;

((1) a second switch-over switch;

(e) a pair of tap terminals;

(f) a finst switch-over resistor means conductively connecting one of said pair of tap terminals to said first switch-over switch;

(g) a second switch-over resistor means conductively conneting the other of said :pair of tap terminals to said second switch-over switch;

(h) a first saturable reactor conductively connecting said one of said paid of tap terminals to said first main switch;

(i) a second saturable reactor conductively connecting said other of said pair of tap terminals to said second main switch;

(j) a first magnetizing current control resistor conductively connecting the end of said first saturable reactor remote from said one of said pair of tap terminals to the end of said first switch-over resistor means remote from said one of said paid of tap terminals; and

(k) a second magnetizing current control resistor conductively connecting the end of said second saturable reactor remote from said other of said pair of tap terminals to the end of said second switch-over resistor mean remote from said other of said pair of tap terminals.

2. A transfer switch for tap changers for regulating transformers comprising:

(a) a first main switch means including a pair of movablecontacts adapted to be operated sequentially and to establish lparallel paths;

(b) a second main switch including a pair of movable contacts adapted to be operated sequentially and to establish parallel current paths;

(c) a first switch-over switch;

(d) a second switch-over switch;

(e) a pair of tap terminals;

(f) a first switch-over resistor means conductively connecting one of said pair of tap terminals to said first switch-over switch;

(g) a second switch-over resistor means conductively connecting the other of said pair of tap terminals to said second switch-over switch;

(h) a first saturable reactor conductively connecting one of said pair of tap terminals to said first main switch means;

(i) a second saturable reactor conductively connecting the other of said pair of tap terminals to said second main switch means;

(j) a first magnetizing current control resistor having 'a resistance being a multiple of said first switch-over resistor means conductively connecting the end of said first saturable reactor remote from one of said pair of tap terminals to the end of said first switchover resistor means remote from said one of said pair of tap terminals; and v (k) a second magnetizing current control resistor having a resistance being a multiple of the resistance of said second switch-over resistor means conductively connecting the end of said second saturable reactor remote fromsaid other of said pair of tap terminals to the end of said second switch-over resistor means remote from said other of said pair of tap terminals.

3. A transfer switch for tap-changers for regulating transformers coimpnising:

(a) a first main switch including a pair of movable contacts adapted to be operated sequentially and to establish parallel current paths;

(b) a second main switch including a pair of movable contacts adapted to be operated sequentially and to establish parallel current paths;

() a first switch-over switch including a plurality of movable contacts adapted to be operated simultaneously and to establish a plurality of current paths in parallel;

(d) a second switch-over switch including a plurality of movable contacts adapted to be operated simultaneonsly and to establish a plurality of current paths in parallel;

(e) a pair of tap terminals;

( f) a first plurality of switch-over resistors connected to have parallel current paths, each of said parallel current paths being controlled by one of said plurality of movable contacts of said first switch-over switch;

(g) a second plurality of switch-over resistors connected to have parallel current paths, each of said parallel current paths being controlled by one of said plurality of movable contacts of said second switch-over switch;

(h) a first saturable reactor conductively connecting one of said pair of tap terminals to said first main switch means;

(i) a second saturable reactor conductively connecting the other of said pair of tap terminals to said second main switch means;

(j) a first magnetizing current control resistor having a resistance being a multiple of the resistance of said first plurality of switch-over resistors connected in parallel, said first magnetizing current control resistor conductively connecting the end of said first saturable reactor remote from said one of said pair of tap terminals to the end of one of said first plurality of switch-over resistors remote from said one of said pairs of tap terminals; and

(k) a second magnetizing current control resistor having a resistance being a multiple of the resistance of said second plurality of switch-over resistors connected in parallel, said second resistor conductively connecting the end of said first saturable reactor remote from said other of said pair of tap terminals to the end of one of said second plurality of switchover resistors remote from said other of said pair of tap terminals.

4. In combination:

(a) a transformer winding adapted to supply a predetermined load current and having a pair of taps;

(b) a pair of main switches;

(c) a pair of switch-over switches;

' (d) a pair of switch-over resistor means each conductively connecting one of said pair of taps to one of said pair of switch-over switches;

(e) a pair of saturable reactors adapted to be saturated when carrying said predetermined load current each conductively connecting one of said pair of taps to one of said pair of main switches; and

(f) a pair of magnetizing current control resistors each conductively connecting one end of one of said pair of saturable reactors remote from one of said pair of taps to one end of one of said pair of switchover resistor means remote from one of said pair of taps.

5. In combination:

(a) a transformer winding adapted to supply a predetermined load current and having a pair of taps;

(b) a pair of main switches each including a pair of movable contacts adapted to be operated sequentially and to establish parallel current paths;

(c) a pair of switch-over switches;

(d) a pair of switch-over resistor means each conductively connecting one of said pair of taps to one of said pair of switch-over switches;

(e) a pair of saturable reactors adapted to be saturated when carrying said predetermined load current each conductively connecting one of said pair of taps to one of said pair of main switches; and

(f) a pair of magnetizing current control resistors each having a resistance being a multiple of the resistance of each of said pair of switch-over resistor means, each of said pair of magnetizing current control resistors conductively connecting one end of one of said pair of saturable reactors remote from said pair of taps to the end of one of said pair of switch-over resistor means remote from said pair of taps.

6. In combination:

(a) a transformer winding adapted to supply a predetermined load current and having a pair of taps;

(b) a pair of main switches each including a pair of movable contacts adapted to be operated sequentially and to establish parallel current paths;

(c) a pair of switch-over switches each including a plurality of movable contacts adapted to be operated simultaneously and to establish a plurality of current paths in parallel;

(d) a pair of groups of switch-over resistors, the constituent resistors of each of said pair of groups being connected to form parallel current paths controlled by one of said pair of switch-over switches;

(e) a pair of saturable reactors adapted to be saturated when carrying said predetermined load current, each of said pair of saturable reactors conductively connecting one of said pair of taps to one of said pair of main switches; and

(f) a pair of magnetizing current control resistors each having a resistance being a multiple of the resistance of each of said pair of groups of switch-over resistors, each of said pair of magnetizing current control resistors conductively connecting one end of one of said pair of saturable reactors remote from said pair of taps to one end remote from said pair of tapsof one of the constituent resistors of one of said pair of groups of switch-over resistors.

References Cited by the Examiner UNITED STATES PATENTS 2,237,008 4/1941 McNairy 32343.5 2,611,117 9/1952 Hibbard 32343.5 X 3,039,041 6/1962 Jansen 323--43.5 3,174,097 3/1965 Bleibtreu 32343.5

5 LLOYD MCCOLLUM, Primary Examiner.

W, E. RAY, Assistant Examinerv 

1. A TRANSFER SWITCH FOR TAP-CHANGERS FOR REGULATING TRANSFORMERS COMPRISING IN COMBINATION: (A) A FIRST MAIN SWITCH MEANS; (B) A SECOND MAIN SWITCH MEANS; (C) A FIRST SWITCH-OVER SWITCH; (D) A SECOND SWITCH-OVER SWITCH; (E) A PAIR OF TAP TERMINALS; (F) A FIRST SWITCH-OVER RESISTOR MEANS CONDUCTIVELY CONNECTING ONE OF SAID PAIR OF TAP TEMINALS TO SAID FIRST SWITCH-OVER SWITCH; (G) A SECOND SWITCH-OVER RESISTOR MEANS CONDUCTIVELY CONNECTING THE OTHER OF SAID PAIR OF TAP TERMINALS TO SAID SECOND SWITCH-OVER SWITCH; (H) A FIRST SATURABLE REACTOR CONDUCTIVELY CONNECTING SAID ONE OF SAID PAID OF TAP TERMINALS TO SAID FIRST MAIN SWITCH; (I) A SECOND SATURABLE REACTOR CONDUCIGELY CONNECTING SAID OTHER OF SAID PAIR OF TAP TERMINALS TO SAID SECOND MAIN SWITCH; (J) A FIRST MAGNETIZING CURRENT CONTROL RESISTOR CONDUCTIVELY CONNECTING THE END OF SAID FIRST SATURATBLE REACTOR REMOTE FROM SAID ONE OF SAID PAIR OF TAP TERMINALS TO THE END OF SAID FIRST SWITCH-OVER RESISTOR MEANS REMOTE FROM SAID ONE OF SAID PAID OF TAP TERMINALS; AND (K) A SECOND MAGNETIZING CURRENT CONTROL RESISTOR CONDUCTIVELY CONNECTING THE END OF SAID SECOND SATURABLE REACTOR REMOTE FROM SAID OTHER OF SAID PAIR OF TAP TERMINALS TO THE END OF SAID SECOND SWITCH-OVER RESISTOR MEAN REMOTE FROM SAID OTEHR OF SAID PAIR OF TAP TERMINALS. 